Radars extract a variety of information from a scene in addition to the measurement of reflected intensities. One example of such additional information is the identification of moving objects, for example, in the air or on the ground. Some pulsed radar systems include a special mode, sometimes referred to as Moving Target Indication (MTI) mode or Ground Moving Target Indicator (GMTI) mode, to determine that targets are moving. In an MTI or GMTI mode, a pulsed radar system may slow down the azimuth sweep of the radar, so that the radar dwells for an extended period of time at each azimuth angle. This allows the pulsed radar system to determine of the radial velocity of the target towards or away from the pulsed radar system. However, MTI/GMTI mode may degrade the quality of the measurements of reflected radar intensities. Also, the pulsed radar system may not be able to utilize other desired modes while utilizing MTI/GMTI mode.
A frequency modulated continuous wave (FMCW) radar operates in a different manner than a pulsed radar. An FMCW radar modulates the transmitted signal with, for example a linear frequency ramp. The frequency ramp may be repeated at a selected interval. The FMCW radar mixes the received return signal with the transmitted signal. Because the received return signals are time-delayed by the time-of-flight from the radar to the target and back, the output of the mixer is a beat signal whose frequency is proportional to the distance to the target. The frequencies in the beat signal may be much lower than the baseband frequency of the radar. An FMCW radar may use an analog-to-digital converter (ADC) to sample the beat signal. The FMCW radar may determine the frequencies in the spectrum of the digitized beat signal by using a fast Fourier transform (FFT).